1. Field of the Invention
The present invention relates to an automatic regressive (AR) filter and a filtering method thereof, and particularly, to an AR filter which functions as an adaptive filter in a still region of an image and outputs an observed signal unaltered in a moving region of the image in order to remove a blurring phenomenon at the edge of a moving target in that image.
2. Related Art
Generally, a filter used for removing noise of an image signal is classified as one of two: a spatial domain filter and a time domain filter. The spatial domain filter includes an average filter in which the current pixel is replaced by a average obtained by applying a weight to horizontal and vertical adjacent pixels within a window of a predetermined size which bounds an area around the current pixel. The spatial domain filter also includes a median filter, in which pixels of a window are ranked depending on the intensity of each pixel and then the proper intensity is selected as a representative value.
In an average filter, the performance of removing the Gaussian noise increases as the size of the window increases. The quality of image is reduced, however, due to a blurring phenomenon at the edge of a target display on a screen. The median filter can preserve the edge due to its strong effect on impulsive noise, however, it is inferior at removing Gaussian noise. In addition to the above filters, there is a LEE filter for varying a weight using the variance of noise in the image.
When applying the spatial domain filter to a continuous moving image, much hardware is required for getting window data in the vertical direction, and the size of the window must be increased to enhance the noise removal capability. Accordingly, it is difficult to implement a real-time process. Thus, the spatial domain filter is applied to a still image.
On the other hand, the time domain filter can be implemented recursively, unlike the spatial domain filter, and provides good noise removal using less hardware. Also, since the edge of the still target of the screen can be preserved well, the time domain filter is often used as a real-time noise removing filter for a moving picture. The time domain filter, however, also causes the blurring at the edge of the moving target as the noise removing capability thereof increases. Thus, the time domain filter is not suitable to be used in an automatic monitoring/sensing apparatus to observe a moving target.